As the age of the population continues to escalate and the complexity of the surgical procedures required by these patients increases, the need for invasive hemodynamic monitoring for protracted periods of time continues to expand. Elderly patients suffering from multiple medical illnesses who are status post complex surgical procedures comprise the greatest percentage of occupants in the surgical intensive care units (SICU). These patients are at continued risk of developing overwhelming infections during their stay in the SICU and sepsis continues to be the leading cause of death in this population.
The reason for the increased incidence of infection and sepsis in the SICU patient is multifactorial but includes: immunosuppression, poor nutrition, surgical stress, prolonged intubation, foley catheterization, and the presence of invasive cannulas. Among these, perhaps the most significant are the invasive lines which frequently predispose to the problem commonly known as line sepsis. The magnitude of this problem is greatly under appreciated. If one considers the fact that Maki found only 15 colony-forming units (CFU) present on the catheter were required to precipitate a sepsis in patients with a central line, it is not surprising that large numbers of patients develop this condition. Clearly the longer an invasive cannula is present and the greater the number of such cannula, the more likely an infection is to occur.
Several conditions must be met for a line sepsis to occur and these conditions can be organized into an operational mechanism which results in a line sepsis. First, organisms must enter and then adhere to the cannula. Once localized within the catheter, bacteria remain relatively protected from the patients' defense against infection. Organisms simply injected into a patient can be effectively eradicated by the host while organisms sequestered in the cannula may escape the natural immune defenses of the patient. From this protected nidus, the bacteria can multiply, establish a colony, and spawn generations of organisms. These micro-organisms then enter the patient from the line repeatedly if not continuously. While patients may be able to eradicate the small initial numbers of organisms released, as the colony increases in size, they are soon overwhelmed by endlessly increasing numbers of bacteria released, ultimately rendering the patient bacteremic and finally septic.
There are five conditions within this operational mechanism and interrupting any one of them effectively eliminates the potential for infection to occur. Organisms must gain access to the system. The bacteria must be able to adhere to the catheter. There must be a nutrient supply which supports bacterial growth. The bacteria must be able to reach the patient from the location of the colony. The organism must be pathogenic in the numbers reaching the patient. If any one of these requirements were eliminated, this mechanism could not operate and line sepsis could not occur.
There is presently no material available able to prevent adherence of the bacteria to the cannula. Once inside the system, there is no way to preclude their replication if the bacteria are presented with a nutrient supply. Such a nutrient supply will always be present in cannulas which have had blood in them. This results from the fact that residual blood will remain in the catheter once a sample is collected regardless of how carefully the line is flushed. TPN also represents a source of nutrients. Indeed lines never exposed to blood or TPN have a lesser association with sepsis.
The only reasonable way to interrupt this mechanism is to prevent the catheter from being seeded in the first place. Since arterial lines are used to sample blood, there is no way to prevent this residual material from collecting in the system. Furthermore, because these catheters are indwelling and used repeatedly, microorganisms have easy access to the patient once they colonize the system. Virtually any bacteria given in adequate dose will be pathogenic, and current use of antibiotics in hospitalized patients selects for more pathogenic organisms. Hence the only point at which the mechanism can be interrupted is at prevention of inoculation by completely excluding bacteria from entering the system in the first place.
Previously there has been no way to preclude clinicians from introducing the organisms in the currently available OPEN systems. Even when sterile technique is strictly maintained, repetitive manipulation of the line will eventually result in its contamination. The fact that Maki has found that as few as 15 organisms in the catheter can result in a line sepsis clearly demonstrates that introducing even small numbers of bacteria into these systems has profound implications for the patient.
Open systems offer an avenue through which lines can be inoculated with a microorganism, thereby providing a source of contamination which must eventually render a patient septic. Efforts to develop closed systems to address the problem of line sepsis have been made, but have not been readily accepted by clinicians. For example, U.S. Pat. No. 4,865,583 to Tu describes a closed intravenous infusion and blood sampling system comprising a three-way valve and a diaphragm-sealed blood sampling apparatus connected to intravenous infusion and catheter tubing and a flushing syringe having sterilized connections.
U.S. Pat. No. 5,148,811 describes an apparatus and method for sampling blood and monitoring blood pressure wherein positive pressure is utilized to force saline unidirectionally into a patient, and provides a valve for partially reversing the flow, allowing entry of blood into the tubing for sampling, but providing a waste collection bag for preventing return of saline into its source reservoir.
Various other systems have been described for directing blood flow and sampling blood in a manner which reduces the possibility of contamination. See for example U.S. Pat. Nos. 4,981,140; 5,203,775; 5,221,271; and 5,417,673. However, each of the above-described inventions concerns systems that necessarily allow introduction into the system of an exogenous source of potential contamination, effectively representing an open system. In addition, these previously described systems do not provide a means for flushing blood that may be retained in the collection port following blood sampling without also flushing possible contaminants into the cannula where they can multiply unrestrained.
While currently available systems have tried to prevent the injection of contaminated material into the patient, all have failed because they have not addressed the central fact they are open systems. Since the system is open, even for a single event, e.g., sampling blood once from the patient, care givers accessing the line will eventually inoculate it with exogenous microbes, no matter how cautious and meticulous they may be. As an aside it should be remembered that "sterile" technique is really not sterile at all. It simply represents the best attempt possible to exclude micro-organisms; the number of organism is only reduced to the lowest level possible. Therefore the line will ultimately be inoculated with small numbers of organisms. Once inoculated the bacteria find an environment replete with nutrients in the form of residual blood. These organisms then multiply in the system. By contrast, the subject invention concerns a system having a one-way valve configured in the blood collection line which prevents entry of any exogenous microorganisms into the cannula. In addition, the subject invention advantageously provides a plurality of channels for diverting flow of fluid from the main cannula line and providing separate and continuous flushing of the blood sampling and monitoring systems.